Femtosecond Laser Fabrication of Microholes in Photosensitive Glass

Microholes were fabricated inside a bulk photosensitive glass(FOTURAN)by focused femtosecond laser irradiation at 775 nm wavelength,followed by programmed heat treatment and wet chemical etching in 8% ultrasonic solution of hydrofluoric(HF)acid for 50 minutes.The focused irradiation was performed by femtosecond-laser longitudinal writing geometry,with upward direction from 500 μm below the surface.The morphologies of formed microholes were analyzed by optical and scanning electron microscopy.It is observed that microholes with circular cross section and clear edge are obtained inside FOTURAN and their diameters are measured to be several tens microns.The maximal aspect ratio value measure of microholes at 7 is achieved.By varying the average laser fluence in a wide range of 2.3~36.2 J/cm2 and the writing velocity in 100~1 000 μm/s,the influences of the incident femtosecond laser parameters on the formation of microholes were experimentally characterized.It is found that the writing velocities hardly affect the microhole diameter,while relatively lower incident laser fluences result in higher aspect ratio,circular cross-section and smoother wall and the possible reason is discussed.